1. Field of the Invention
The present invention relates to a liquid electrophotographic imaging system and, more particularly, to a liquid electrophotographic imaging system having an improved structure which prevents a carrier used during development from condensing at an output window of an optical scanning unit.
2. Description of the Related Art
In general, a liquid electrophotographic imaging system is an apparatus for forming an image on a photoreceptor medium such as a photoreceptor web or a photoreceptor drum by developer which is a mixture of a solid toner and a liquid carrier, and transferring the image to a sheet of print paper.
Referring to FIG. 1, a general liquid electrophotographic imaging system includes a photoreceptor medium 20 such as a photoreceptor web circulating around a predetermined path by being supported by a steering roller 11, a driving roller 13 and a transfer backup roller 15. The photoreceptor medium 20 is charged by a charger 23 to a predetermined electric potential. The charged electric potential varies in response to the light scanned by a laser scanning unit (LSU) 30. A discharger 21 provided around the photoreceptor web 20 resets the electric potential formed on the photoreceptor medium 20. The charger 23 charges the photoreceptor web 20 to a predetermined electric potential. The laser scanning unit 30 forms an electrostatic latent image corresponding to each color by scanning light onto the photoreceptor medium 20. Development units 25 are provided, one for each corresponding color of yellow (Y), magenta (M), cyan (C) and black (K). An image is formed in an area where an electrostatic latent image corresponding to each color is formed. That is, each development unit 25 carries solid toner of a certain color using the liquid carrier to a development gap between the development unit 25 and the photoreceptor medium 20. An image is formed in an area corresponding to the electrostatic latent image due to a difference between the electric potential applied to the photoreceptor medium 20 and the electric potential for development. Excess carrier left over on the photoreceptor web 20 is removed by a drying unit 27. The image formed on the photoreceptor web 20 is transferred to a print paper P by a transfer unit 29.
The structural elements including the photoreceptor medium 20, the laser scanning unit 30, and the development unit 25 are housed in a cabinet 10 having an inlet and an outlet through which the print paper P enters and exists, respectively. The cabinet 10 is for preventing the carrier which exists in a gaseous state by passing the drying unit 27 and the transfer unit 29 after being used during development from escaping to the outside .
Referring to FIGS. 2 and 3, the laser scanning unit 30 is comprised of a driving source 51, a deflection disk 55 having a plurality of sectors, each having a hologram pattern, a light emitting means 40 disposed at one side of the deflection disk 55 for emitting light to the deflection disk 55, an optical path changing means for changing a proceeding direction of the light deflected by the deflection disk 55, and a housing 31 housing the above structural elements and having transparent windows 35 through which scanning light passes. To correspond to a color image, the light emitting means 40 is comprised of first through fourth light sources 41, 43, 45 and 47 suitable for yellow, magenta, cyan, and black, respectively. The light emitted from each of the first through fourth light sources 41, 43, 45 and 47 is incident on a predetermined position of the deflection disk 55. Here, the light path changing means includes a plurality of flat mirrors M.sub.11, M.sub.12, M.sub.21, M.sub.22, M.sub.31, M.sub.32, M.sub.41, and M.sub.42, other flat mirrors M, curved mirrors CM.sub.1, CM.sub.2, CM.sub.3, and CM.sub.4, and holographic optical elements HOE.sub.1, HOE.sub.2, HOE.sub.3, and HOE.sub.4. The curved mirrors CM.sub.1 -CM.sub.4 are for focusing and reflecting scanning lines input through a plurality of optical paths via the flat mirrors M to make and maintain the scanning lines emitted to be parallel to each other. Also, the curved mirrors CM.sub.1 -CM.sub.4 correct diffraction of incident light due to the holographic pattern of the deflection disk 55 and bowing, a phenomenon in which the scanning line is bent, caused by forming the scanning line by rotation of the deflection disk 55. By diffracting and transmitting the scanning line incident on the holographic optical elements HOE.sub.1 -HOE.sub.4 at a predetermined angle, the scanning line is made to proceed in a direction perpendicular to the photoreceptor medium 20.
The housing 31 allows the above optical elements to be installed at predetermined positions inside the cabinet 10 and prevents the optical path changing means from being contaminated by developer in the cabinet 10. The scanning lines proceeding toward the photoreceptor medium 20 via the holographic optical elements HOE.sub.1 -HOE.sub.4 pass through the transparent windows 35.
The carrier in a gaseous state and/or vapor in the cabinet 10 adheres to an inside wall of the cabinet 10, the housing 31 of the laser scanning unit, and the transparent windows 35. Particularly, the carrier N and/or vapor (H.sub.2 O) condensed on the transparent windows 35 form drops due to the surface energy of the transparent windows 35. Such formation of drops is called beading.
When there is beading in an area where the scanning line 100 (see FIG. 3) passes, the scanning line disperses. Thus, as shown in FIG. 4, an unclear image 111, i.e., color spreading on a desired image 110, is formed on the photoreceptor medium 20.
Therefore, since the carrier and/or vapor is formed on the transparent windows and the scanning lines disperse due to beading, resolution of an image is lowered and print quality is deteriorated.